1. Field of the Invention
The present invention relates to a linear guide apparatus for use in machine tools, industrial machines, etc.
2. Description of the Related Art
A linear guide apparatus, as a linear guide for use in a machining center as a machine tool, a robot as an industrial machine, etc., has been known. As shown in FIGS. 16, 17A and 17B, this linear guide apparatus comprises a guide rail 2 having a rolling-element rolling groove 1 formed on both sides thereof in the axial direction and a slider 3 which fits in the guide rail 2. Provided on the inner surface of the slider 3 is a rolling-element rolling groove 4 disposed opposed to the rolling-element rolling groove 1 of the guide rail 2. A number of rolling elements 5 are rollably interposed between the rolling-element rolling grooves 1, 4. In this arrangement, the slider 3 makes relative movement with the rolling elements 5 along the axis of the guide rail 2.
In this linear guide apparatus, the slider 3 has an end cap 6 provided on both axial ends thereof. The end cap 6 has a circulating path 7 forming a curved path communicating to the rolling-element rolling grooves 1, 4 for circulating rolling elements.
As shown in FIG. 18, the slider 3 may have a slow inclination called crowning portion 8 provided at both ends thereof for relaxing stress concentration. It is known that the provision of the crowning portion 8 makes it possible to enhance durability. On the other hand, the crowning portion 8 has an effect on the degree of change of sliding resistance of the slider 3 of the linear guide apparatus during movement. This change of sliding resistance has an adverse effect on the performance of machines comprising the linear guide apparatus. For example, the positioning properties of the machines are deteriorated to disadvantage. It has thus been desired to reduce the change of sliding resistance.
However, the selection of the crowning form for inhibiting the change of sliding resistance has heretofore been often experimentally made. Therefore, in order to realize a rolling linear guide having a reduced change of sliding resistance, production on a trial basis and by experiments must be repeated, requiring much labor.
The present invention has been worked out under these circumstances. An aim of the present invention is to provide a linear guide apparatus which has a reduced change of an axial component of contact load of a slider at a crowning portion with movement of rolling elements to exhibit a reduced change of sliding resistance.
Another aim of the present invention is to provide a linear guide apparatus suitable for uses in situations requiring a reduced change of sliding resistance such as in an electric discharge machine, a mold processing machine, a drawing device, a semiconductor producing machine (exposing device), and a precision measuring instrument.
In order to accomplish the aforementioned aims of the present invention, the present invention lies in a linear guide apparatus having a guide rail having a rolling-element rolling groove formed on a side thereof along an axial direction, and a slider having a rolling-element rolling groove disposed so as to be opposed to the rolling-element rolling groove of the guide rail, the slider moving relatively in the axial direction of the guide rail with rolling elements rollably interposed between the two rolling-element rolling grooves, and a crowning portion disposed on both axial ends of the rolling-element rolling groove of the slider, wherein a maximum value of a total load in an axial direction applied on the crowing portions on the axial ends of the slider by the rolling elements is set to be smaller than a maximum value of load in the axial direction applied on one of the crowning portions of the slider by one rolling element.
In other words, the linear guide apparatus is arranged such that the load in the axial direction applied on the rolling elements at the right and left crowning portions cancel each other. In this arrangement, the sum of the load applied on the rolling elements at the right and left crowning portions is set to be smaller than the maximum value of the load in the axial direction applied on the slider at one of the crowning portions by the rolling elements.
At the portion free of crowning portion, the direction of contact load of the rolling elements with the rolling groove is perpendicular to the axial direction. Therefore, the contact load at this portion has no axial component.
However, at the portion having a crowning portion, the contact load of the rolling element with the rolling groove has an axial component. The magnitude of this axial component normally changes with the movement of the rolling elements. This is attributed to the fact that the arrangement of the crowning portion causes the change of the rolling elements and the rolling groove and hence the change of the contact load and the direction of contact of the rolling elements with the rolling groove changes.
The change of the axial load generated at the crowning portion causes the sum of the load in the axial direction applied on the slider by the crowning portion at both ends to change with the movement of the slider (i.e., movement of the rolling elements). This change of the load in the axial direction directly leads to the change of the sliding resistance of the slider.
In accordance with the present invention, these axial loads can cancel each other at the right and left crowning portions. In this arrangement, the axial load acted on the slider can be predetermined to be smaller than the maximum value of the load in the axial direction applied on the slider at one of the crowning portions. In other words, the change of the sliding resistance of the slider can be reduced.
In addition to this, according to the present invention, it is preferable that a linear guide apparatus having a guide rail having a rolling-element rolling groove formed on a side thereof along in an axial direction, a slider having a rolling-element rolling groove disposed so as to be opposed to the rolling-element rolling groove of the guide rail, the slider moving relatively in the axial direction of the guide rail with rolling elements rollably interposed between the two rolling-element rolling grooves, and a crowning portion disposed on the both axial ends of the slider, wherein the crowning portion is a linear crowning having a constant inclination angle xcex8 and satisfying the following relationship:
0 less than xcex8(Nxc3x97txe2x88x92Le) less than xcex4o
wherein N represents an integer of 1 or more; t represents the distance between centers of the rolling elements (with separator) or a diameter of the rolling element (free of separator); Le represents the length of the non-crowning portion; and xcex4o, represents preload amount (diameter of rolling element based on the diameter of rolling element which gives zero elastic deformation at the non-crowning portion).
Further, according to the present invention, it is preferable that a linear guide apparatus having a guide rail having a rolling-element rolling groove formed on a side thereof along in an axial direction, and a slider having a rolling-element rolling groove disposed so as to be opposed to the rolling-element rolling groove of the guide rail, the slider moving relatively in the axial direction of the guide rail with rolling elements rollably interposed between the two rolling-element rolling grooves, and a crowning portion disposed on the both axial ends of the slider, wherein the crowning portion is an arc crowning having a constant radius R and satisfying any of the following relationships (1) to (3):
Ntxe2x88x92Lexe2x89xa60.5t and 0.5{square root over (2Rxcex4o)} less than Nxc3x97txe2x88x92Le less than 1.5{square root over (2Rxcex4o)};xe2x80x83xe2x80x83(1)
0.5t less than Nxc3x97txe2x88x92Le less than 1.5{square root over (2Rxcex4o)};andxe2x80x83xe2x80x83(2)
t less than {square root over (2Rxcex4o)}xe2x80x83xe2x80x83(3)
wherein N represents an integer of 1 or more; t represents the distance between centers of the rolling elements (with separator) or the diameter of the rolling element (free of separator); Le represents the length of the non-crowning portion; and xcex4o represents preload amount (diameter of rolling element based on the diameter of rolling element which gives zero elastic deformation at the non-crowning portion).